This invention relates generally to controlling the operation of equipment for processing materials to produce a product which includes aggregate materials and a volatile component. More particularly, the invention relates to an integrated system for controlling the operation of processing equipment based upon an analysis of the weight ratios of different sizes of aggregate materials to the total quantity of aggregate materials remaining after the volatile component has been removed. A preferred embodiment of the invention relates to an integrated system for controlling the operation of an item of processing equipment based upon an analysis of the ratio of the amount of the volatile component contained in a sample of the product to the total weight of the sample of the product. The invention is useful, for example, especially in its preferred embodiment, in controlling the relative composition of the components of hot mix asphalt.
Sampling of various aggregate materials is commonly required in the construction, mining and other industries to insure that the materials meet the required specifications for quality, composition, and/or gradation. Samples of products containing aggregate materials may be taken at various stages during the processing or manufacturing thereof for analysis to insure that the proper particle sizes of aggregate materials are being produced. During rainfall and other adverse weather conditions, it may be difficult to analyze the particle sizes of a product containing aggregate materials to insure that the proper particle sizes of the aggregate materials are being produced. In addition, when a product includes a volatile component other than water, such as the asphalt cement in a hot mix asphalt product, it is also desirable to sample the product for analysis to insure that the desired proportion of asphalt cement to the aggregate component of the product meets a predetermined standard, such as for example, 3-5% by weight.
Samples of products containing aggregate materials and a volatile component, such as for example, wet aggregate materials and hot mix asphalt, may be taken from conveyors, trucks, barges, railcars or other transport devices, or from product stockpiles, silos, or other storage facilities. Such samples may be taken manually or automatically, and they may be taken from quantities of products produced by batch or continuous processes.
It is common for producers of products containing aggregate materials to sample their product at several stages, including the shipping stage. In addition, the purchaser will almost always sample at least a portion of the incoming shipments before unloading them to insure that they are acceptable. Products containing aggregate materials that are hauled by truck are usually sampled by hand shoveling a sample portion from various locations in the product load in the truck bed, in order to obtain a representative sample. Because the aggregate in the product may segregate by size as it is being loaded and hauled, however, hand sampling in this way makes it difficult to obtain a representative sample. It is generally necessary to remove a portion of the surface material from several locations in the truck bed in order to obtain a sample portion from therebeneath. However, when the aggregate product is bituminous paving material such as hot mix asphalt, its surface temperature may be as high as 250-300xc2x0 F., which makes hand sampling at least uncomfortable and potentially dangerous. Furthermore, a worker who is charged with the responsibility of obtaining a hand sample from a hot mix asphalt truck will not likely be willing and may not be able to spend the time to take sample portions from various locations on the load in the truck bed to insure that he gets a representative sample. Nevertheless, the standard practice for sampling bituminous paving mixtures from truck transports is to take several portions of a sample from each truck using a flat-bottom scoop or a square-nose shovel.
ASTM Designation D 979-96 specifies that at least three approximately equal increments should be taken from each truck load of bituminous paving materials sampled. Various state highway departments impose additional requirements on the sampler of asphalt concrete, in an effort to insure that representative samples are obtained. For example, the Georgia Department of Transportation Sampling Procedure GSP-15 specifies that hand samples may be taken only after the xe2x80x9cconexe2x80x9d of material in the bed of the truck is first shoveled off to a depth such that the resulting flat area is at least 60% as wide as the truck and at least six inches deep. Wyoming Department of Transportation Sampling Procedure 830.0 requires that for smaller trucks, a sample area must be prepared by removing the top 2-4 inches from each quarter of the load, while for larger trucks, at least two transverse trenches must be excavated across the load in the truck bed. The sample is then removed by pushing the shovel into each cleared area or trench at a 45xc2x0 angle. Illinois Department of Transportation Sampling Procedure 4.7.1 requires that an equal amount of material is to be taken from locations approximately one foot below the top of each pile in the truck bed, at quarter points around the pile""s circumference. Mississippi Department of Transportation Field Testing Procedure TMD-11-77-00-000 requires that at least three samples be taken from specified locations in the truck after first removing the top 2-3 inches of material at each sample point. All of these-procedures require that the sampler work for a significant period of time in the bed of the truck atop the load of hot mix asphalt. Complying with such procedures is uncomfortable and may be dangerous, which makes proper sampling problematic.
Once a sample of product comprised of various aggregate materials and a volatile component (which may be water) is obtained, analysis is often required to insure that the materials meet the required specifications for composition and/or gradation. Many such products include mixtures or blends of components having various particle sizes. Thus, for example, certain coal and coke products and industrial catalytic powders are sold having various particle sizes in specified ranges by weight. Crushed stone products that are used in the construction of roadways may also include mixtures or blends of several particle sizes in various specified ranges, depending on the anticipated use. Several such crushed stone products, as well as sand and/or other aggregates and other additives, including asphalt cement as a volatile component, are combined in specific weight percentages in the manufacture or processing of bituminous paving mixtures.
It is known that the particle size distribution in a quantity of aggregate materials may be determined more-or-less automatically. Thus, for example, U.S. Pat. No. 3,439,800 of Tonjes, U.S. Pat. No. 5,059,310 of Fischer et al. and U.S. Pat. No. 5,222,605 of Pogue describe methods and devices for automatically determining the proportionate amounts of various particle sizes of such a product. Such methods and devices, however, do not contemplate control of equipment such as a rock crusher that is employed in the processing or manufacturing of the product which includes aggregate materials and a volatile component.
Finally, heating devices have been used to facilitate the sampling and analysis of products which include aggregate materials. Such heating devices remove the combustible components of a product which includes aggregate material. By heating the product to a level sufficient to burn off the combustible components, the heating devices effectively isolate the aggregate materials contained in the product for more accurate sampling and analysis of the aggregate material distribution. Examples of such prior art heating devices are contained in U.S. Pat. No. 5,081,046 of Schneider, U.S. Pat. No. 6,000,935 of Regimand, et al., U.S. Pat. No. 4,276,093 of Pickermann and U.S. Pat. No. 6,054,323 of Troxler. Some of such heating devices include rotating and/or tilting containers in which the sample may be heated. Such devices are described in U.S. Pat. No. 5,785,516 of Tanaka and U.S. Pat. No. 5,947,720 of Kelly. None of the devices described in these prior art patents, however, is part of a method and apparatus for controlling an item of equipment that is employed in processing or manufacturing the product. It would be desirable if such a method and apparatus could be developed for control of an item of equipment that is employed in the processing or manufacturing of a product which includes aggregate materials and a volatile component.
Among the advantages of the invention is that it may be utilized control an item of equipment used in processing a product which includes aggregate materials and a volatile component in order to maintain the relative ratios of aggregate materials of various particle sizes in the product within predetermined standards. Another advantage of a preferred embodiment of the invention is that it may be used to control an item of equipment that is used in processing such a product in order to maintain the ratio of the amount of the volatile component of the product to the amount of aggregate materials in the product within a predetermined standard.
Additional advantages of this invention will become apparent from an examination of the drawings and the ensuing description.
As used herein, the term xe2x80x9caggregate materialsxe2x80x9d refers to materials that may be transported in bulk and are produced and/or sold in particulate form with or without other additives, such as, for example, crushed limestone and other types of crushed stone, bituminous paving mixtures such as hot-mix asphalt and cold mix, gravel, sand, lime, coal, coke, metallic oxide and other powders used for catalytic or other reactive purposes, and similar materials such as grain, pellets, and fertilizer.
As used herein, the terms xe2x80x9casphalt cementxe2x80x9d and xe2x80x9casphalt binderxe2x80x9d refer to a black or brown tar-like substance, a type of bitumen that occurs naturally or is obtained from the distillation of coal tar, wood tar or petroleum.
As used herein, the terms xe2x80x9casphalt concretexe2x80x9d and xe2x80x9chot-mix asphaltxe2x80x9d refer to a bituminous paving mixture that is prepared, using hot asphalt cement or asphalt binder, in a hot-mix asphalt plant.
As used herein, the term xe2x80x9cbituminous paving mixturexe2x80x9d refers to a mixture of various aggregates, including crushed stone, sand, lime and the like, with asphalt cement or asphalt binder, which mixture is prepared for paving purposes.
As used herein, the term xe2x80x9ccold mixxe2x80x9d refers to a bituminous paving mixture that is prepared without the use of hot asphalt cement or asphalt binder.
As used herein, the terms xe2x80x9ccontrol an item of equipmentxe2x80x9d and xe2x80x9ccontrolling an item of equipmentxe2x80x9d refer to adjusting or otherwise affecting the operation of an item of equipment, or changing the composition or gradation of a product produced or material processed thereby.
As used herein, the term xe2x80x9cthe net weight of the containerxe2x80x9d refers to the weight of the contents of the oven container.
As used herein, the term xe2x80x9cproduct which includes aggregate materials and a volatile componentxe2x80x9d refers to a product comprised of one or more aggregate materials having a plurality of particle sizes in a predetermined ratio by weight and at least one volatile component such as, for example, asphalt cement or water.
The invention comprises a system and method for controlling the operation of an item of equipment for processing materials in connection with the production of a product which includes aggregate materials and a volatile component. The system includes an oven, a gradation assembly, means for transporting aggregate materials from the oven to the gradation assembly, and means for controlling the operation of an item of equipment for processing aggregate materials if certain conditions are found to exist. The oven includes a container defining an interior space and having a receiving end for receiving a sample of the product and a closed end opposite the receiving end. The oven also includes a heat source for heating a sample of the product in the container to remove the volatile component from the sample. The oven further includes a weighing mechanism for determining the net weight of the container, means for determining the ratio of the net weight of the container before the sample is heated to the net weight of the container after the sample is heated, and means for determining if the ratio of the net weight of the container before the sample is heated to the net weight of the container after the sample is heated meets a predetermined standard. The gradation assembly includes a plurality of gradation screens and a frame that is adapted to support the gradation screens in a generally horizontal attitude in a stacked arrangement whereby each screen in the stack has screen openings that are smaller than those of the screen immediately above it in the stack. The gradation assembly also includes means for vibrating the screens and a weighing pan that is adapted to determine the weight of aggregate materials. The gradation assembly also includes means for sequentially depositing the aggregate materials that are retained on each screen, or that pass through all of the screens, in the weighing pan, means for determining the ratios of the weights of the different groups of the aggregate materials that are retained on each of the screens or that pass through all of the screens to the total weight of the aggregate materials, and means for determining if each of these ratios meets a predetermined standard.
The system of the invention also comprises means for transporting the components of the product remaining in the oven after the sample is heated to the gradation assembly, and means for controlling the operation of a first item of equipment for processing aggregate materials if one of the ratios of the weight of the aggregate materials that are retained on any of the screens or that pass through all of the screens to the total weight of the aggregate materials deposited in the gradation assembly fails to meet a predetermined standard. In a preferred embodiment of the invention, the system also comprises means for controlling a second item of equipment for mixing a volatile component of the product, such as asphalt cement, and aggregate materials if the ratio of the weight of the volatile component to the total weight of a sample of the product fails to meet a predetermined standard.
In order to facilitate an understanding of the invention, the preferred embodiments of the invention are illustrated in the drawings, and a detailed description thereof follows. It is not intended, however, that the invention be limited to the particular embodiments described or to use in connection with the apparatus illustrated herein. Various modifications and alternative embodiments such as would ordinarily occur to one skilled in the art to which the invention relates are also contemplated and included within the scope of the invention described and claimed herein.